Means for heating filaments



July 21, 1931. H. J. ROUND MEANS FOR HEATING FILAMENTS Filed Oct. 14, 1921 Patented July 21, 1931 E'I'E STATES ATE?! OFFiEZE HENRY JOSEPH ROUND, OF LONDON, ENGLAND, ASSIGNOR TO RADIO CORPORATION OF AMERICA, A CORPORATION OF DELAWARE MEANS FOR HEATING FILAMENTS Application filed October 14, 1921.

Hitherto the filament contained within a vacuous bulb, such as is used, for instance, as a valve, an amplifier or a generator in wireless telegraphy and telephony, has been heated by a current conveyed to it by wires sealed into the envelope of the bulb. There is, however, at present a tendency to use heavier and heavier currents for heating such filaments and this tendency leads to a difiiculty in sealing the leading in wires.

My invention is illustrated in the single figure of the accompanying drawing, wherein B represents a thermionic device containing plate P, grid G and filament F. According to this invention I dispense with any necessity for sealing such leading in wires and I connect the two ends of the filament F to the two ends of a small coil of wire C which is entirely contained within the bulb B, the latter being preferably provided with an extension E for the purpose of receiving this coil. I then surround this coil with a p1- mary winding W outside the bulb or rather the extension of the bulb E so that when an alternating or intermittent current, preferably of a comparatively high frequency, is passed through the primary, currents suificient to heat the filament to the desired extent are induced in the coil O within the bulb.

The filament may be connected to an external circuit by an ordinary leading in wire L sealed into the glass of the bulb in the usual manner.

Having described my invention what I claim is 1. The combination of an evacuated container, a filament adapted to be heated located within said container, a coil located within said container and connected to said filament, a winding external to said container and arranged in inductive relation with said coil through the materialof said container and means for controlling the potential of said filament including a single conductor passed through said envelope and connected to said filament.

2. The combination with a vacuum tube comprising an envelope containing a filament adapted to be heated, an extension to Serial No. 507,756.

said envelope, a coil located within said extension connected to said filament, a second coil surrounding the said extension and in inductive relation with said first named coil, and a lead-in conductor connected to said filament.

3. The combination with an evacuated envelope containing a filament adapted to be heated, said envelope being provided with an extension, a coil located within said extension connectors between said coil and said filament, a second coil external to said envelope surrounding said extension and in inductive relation with said first mentioned coil, and a single lead-in from one of said connectors to the outside of said container.

4. A vacuum tube and cathode means, a container therefor, and heating means therein, comprising a coiled conductor positioned within an extension of said container and having its ends connected to the ends of said cathode, a second coil surrounding said extension and said first mentioned coiled conductor and adapted to be energized by alternating currents whereby heavy currents are induced in said first men' tioned coiled conductor and cause a flow along said cathode, and a single conductive connection through said contalner to said cathode.

5. The means for heating a cathode within a container, comprising a coil connected thereto and positioned entirely within said container, and a second coil positioned entirely outside of said container and insulated therefrom and adapted to be energized by an alternating current and to induce an alternating current in said interior coil, and a single conductive connection to said cathode through said container, whereby the heavy heating currents are induced entirely within said container and the electron stream current only is led through said conductive con nection.

6. A vacuum tube device comprising an evacuated vitreous container, an electrode assembly therein adapted to produce control and receive an electron stream and having respective terminals, a coiled conductor also wholly within said envelope and having its ends connected to certain ones of said terminals, and inductive means Wholly Without said envelope adapted to cooperate with said coiled conductor by magnetic induction through said container and a single lead-in 5 Wire from said coiled conductor to the outside of said container.

HENRY JOSEPH ROUND. 

